Where to start? Want to build 30 day programmable timer to charge batteries

Thread Starter

fabes253

Joined May 18, 2013
6
Hello all,

As we turn to the new age I am finding more and more that many of my products, for example 80V lawn equipment, battery pack jump starters, and rechargeable batteries etc.. require some sort of power cycle/maintain around every 30 days or so.

My goal is to create (cheaply) a 'set it and forget it' system where I can essentially have a power strip turn on every 30 days. My idea is that I would have all my charges plugged into the power strip, and every 30 days I would like the charger to turn on for 3-5 hours. If there was a way to also discharge the batteries I think that would be a bonus as some instructions say the battery should be depleted and recharged.

The only chargers I have found are up to 7 days, so was hoping there was a neat hack or way to adjust it to work for 30 days.

I would really appreciate any ideas, I can follow good instructions but I'm not too tech savvy on my own, so keeping it simple would ideal.
 

Thread Starter

fabes253

Joined May 18, 2013
6
Thanks Yaakov, I beleive you're right so I will actually follow your advice. I rechecked my 80V manual and indeed it just says to store it in a room temperature location. I do have one lead-acid battery that the manual does in fact say to charge every 30 days and after each use of course. I don't know a great deal about batteries and I am not familiar with the floating you mention. What would you suggest then for this lead-acid battery (jump starter)?
 

Papabravo

Joined Feb 24, 2006
16,107
Thanks Yaakov, I beleive you're right so I will actually follow your advice. I rechecked my 80V manual and indeed it just says to store it in a room temperature location. I do have one lead-acid battery that the manual does in fact say to charge every 30 days and after each use of course. I don't know a great deal about batteries and I am not familiar with the floating you mention. What would you suggest then for this lead-acid battery (jump starter)?
For scheduling on that time scale, it seems to me that any general purpose platform like an Arduino with appropriate shields would be up to the job.
 

Ian0

Joined Aug 7, 2020
2,192
Lead acid batteries intended for cyclic use will last much longer if they are charged up once a month and left, rather than being left permanently on float charge. The type that is intended for permanent float charge (i.e. emergency lighting) is not suitable for cyclic use, so is unlikely to be fitted to your lawnmower. Leave your lawnmower battery on float charge all winter and come spring, you'll need a new battery.

Only Nickel chemistry batteries need to be discharged. Don't discharge a lead-acid battery unnecessarily, you'll just use up some of its life.
Nickel chemistry batteries can also be stored in a discharged state.

For your project, if you clock a CD4521 off the mains supply, then divide that again by 8 with three stages of CD4024, you'll get a pulse every 31 days (if you're the other side of the Atlantic, it will be every 26 days), you could use that to start a charger, then turn it off when the batteries are charged. No software required!
 

KeithWalker

Joined Jul 10, 2017
1,779
The simplest and cheapest way to make a programmable long-delay switch is with a couple of old-fashioned electro-mechanical timers. The first one turns on the second one at the same time every day for 1Hr:15Min. That will close the contacts on the second timer once every the 30 days.
I used this system for years to keep the NI-Cad batteries in my RC electric planes and their transmitters topped up for week-end flying.
This would work well for cycling lead-acid batteries.
 
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AnalogKid

Joined Aug 1, 2013
9,248
As above, a couple of 1-minute programmable lamp timers fro ebay or Walmart will do what you want. Ir you *really* want to build something ...

The CD4060 is a 14-bit binary counter with a built-in oscillator. If the oscillator components are selected such that longest output (Q14) cycle is 60 days (so one-half cycle is 30 days), one of the Q7output will have a pulse width of 5.6 hours. The system flow is something like this:

AC power
Wall wart making 5 V or 12 V DC
Timer circuit
Solid State Relay
Output power strip
Battery chargers

ak
 
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Ian0

Joined Aug 7, 2020
2,192
I'd definitely prefer the logic-counter solution. If you write software, how long is it going to take you to test it? If it doesn't work after the first month . . . .
 

AnalogKid

Joined Aug 1, 2013
9,248
Typically for a long range 4060 timer, I have two timing capacitors in parallel, about 100x apart in value, and a 2-pin shunt to disconnect the larger one so the counter runs faster during test. Shunts are cheap. In this case, the fast-mode capacitor would be approx 40,000 smaller than the long-mode cap. This would shift the Q14 output from one output every 30 days to one per second.

You can do the same thing with an unused GPIO pin on a uC, sensing that input bypass some of the timing loops for a faster test result.

ak
 
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